Medical Ultrasound Systems Research Articles

Adaptive field-of-view imaging for efficient receive beamforming in medical ultrasound imaging systems

Quadrature demodulation-based phase rotation beamforming (QD-PRBF) is commonly used to support dynamic receive focusing in medical ultrasound systems. However, it is computationally demanding since it requires two demodulation filters for each receive channel. To reduce the computational requirements of QD-PRBF, we have previously developed two-stage demodulation (TSD), which reduces the number of lowpass filters by performing demodulation filtering on summation signals. However, it suffers from image quality degradation due to aliasing at lower beamforming frequencies. To improve the performance of TSD-PRBF with reduced number of beamforming points, we propose a new adaptive field-of-view (AFOV) imaging method. In AFOV imaging, the beamforming frequency is adjusted depending on displayed FOV size and the center frequency of received signals. To study its impact on image quality, simulation was conducted using Field II, phantom data were acquired from a commercial ultrasound machine, and the image quality was quantified using spatial (i.e., axial and lateral) and contrast resolution. The developed beamformer (i.e., TSD-AFOV-PRBF) with 1024 beamforming points provided comparable image resolution to QD-PRBF for typical FOV sizes (e.g., 4.6% and 1.3% degradation in contrast resolution for 160 mm and 112 mm, respectively for a 3.5 MHz transducer). Furthermore, it reduced the number of operations by 86.8% compared to QD-PRBF. These results indicate that the developed TSD-AFOV-PRBF can lower the computational requirement for receive beamforming without significant image quality degradation.

Development of tissue-equivalent phantoms for biomedical ultrasonic applications

Tissue phantoms are, generally, used in the calibration of therapeutic and diagnostic systems. Thus, Tissue-Mimicking (TM) phantoms are developed and studied here for various ultrasonic output parameters. These phantoms have been developed by using agar-based Tissue-Mimicking Materials (TMM) with alumina as an absorption material. A pulser ? receiver (make Panametrics, Model ? 5800, Waltham, MA 02154, USA) has been used to measure ultrasonic velocity and attenuation coefficient, which were found to be 1540?1550 m/s and attenuation 10.0?35.0 dB/m-MHz at frequencies from 2.5 MHz to 5.0 MHz. These ultrasound test phantoms incorporating TM material are useful in the performance evaluation of medical ultrasound systems.

Doppler ultrasound wall removal based on the spatial correlation of wavelet coefficients

In medical Doppler ultrasound systems, a high-pass filter is commonly used to reject echoes from the vessel wall. However, this leads to the loss of the information from the low velocity blood flow. Here a spatially selective noise filtration algorithm cooperating with a threshold denoising based on wavelets coefficients is applied to estimate the wall clutter. Then the blood flow signal is extracted by subtracting the wall clutter from the mixed signal. Experiments on computer simulated signals with various clutter-to-blood power ratios indicate that this method achieves a lower mean relative error of spectrum than the high-pass filtering and other two previously published separation methods based on the recursive principle component analysis and the irregular sampling and iterative reconstruction, respectively. The method also performs well when applied to in vivo carotid signals. All results suggest that this approach can be implemented as a clutter rejection filter in Doppler ultrasound instruments.

Gaussian wavelet based dynamic filtering (GWDF) method for medical ultrasound systems

In this paper, a novel dynamic filtering method using Gaussian wavelet filters is proposed to remove noise from ultrasound echo signal. In the proposed method, a mother wavelet is first selected with its central frequency (CF) and frequency bandwidth (FB) equal to those of the transmitted signal. The actual frequency of the received signal at a given depth is estimated through the autocorrelation technique. Then the mother wavelet is dilated using the ratio between the transmitted central frequency and the actual frequency as the scale factor. The generated daughter wavelet is finally used as the dynamic filter at this depth. Frequency-demodulated Gaussian wavelet is chosen in this paper because its power spectrum is well-matched with that of the transmitted ultrasound signal. The proposed method is evaluated by simulations using Field II program. Experiments are also conducted out on a standard ultrasound phantom using a 192-element transducer with the center frequency of 5 MHz. The phantom contains five point targets, five circular high scattering regions with diameters of 2, 3, 4, 5, 6 mm respectively, and five cysts with diameters of 6, 5, 4, 3, 2 mm respectively. Both simulation and experimental results show that optimal signal-to-noise ratio (SNR) can be obtained and useful information can be extracted along the depth direction irrespective of the diagnostic objects.

Direction separation in Doppler audio of ultrasound diagnosis equipment: Signal processing for Doppler audio dealiasing

Medical Doppler ultrasound system has time varying spectrum display and Doppler audio stereo output based on blood flow. We examined the digital signal processing system of Doppler audio from a viewpoint of cost and size reduction. We newly developed the direction separation system of Doppler audio processing interlocking with spectrum Doppler image processing for aliasing. We made the target performance, developed three kinds of signal processing systems, and evaluated each system. Consequently, we could know that the complex IIR filter system was excellent in a response and low calculation load. We confirmed the Doppler audio signal processing for aliasing by simulation and could solve the problem caused by conventional system.

System and method for adapting the behavior of a diagnostic medical ultrasound system based on anatomic features present in ultrasound images

A diagnostic medical imaging system is disclosed, such as a diagnostic medical ultrasound system, which uses operational rules or an anatomic model of an anatomical structure as an organizational framework for applying anatomy-specific auxiliary/secondary information. After processing the operational rules on the acquired images or associating the model with the acquired images, adapting/fitting the model to match the images if necessary, the imaging system can associate aspects of the images being acquired with the auxiliary/secondary information, allowing the imaging system to behave as if it “knows” what it is scanning. The auxiliary information may be rules that affect the behavior of the imaging system, or may be the acquired image samples. System behavior may then be automatically adapted or the operator may be prompted to make operational changes.

Novel transmit aperture for very large depth of focus in medical ultrasound B-scan

Obtaining high quality ultrasound images at high frame rates has great medical importance, especially in applications in which tissue motion is significant (e.g., the beating heart). Dynamic focus and dynamic aperture can improve image quality significantly, and they have been implemented on the receive beam in state-of-the-art medical ultrasound systems. However, implementing dynamic focus and dynamic aperture on the transmit beam compromises frame rate. We introduce a novel sinc squared-argument transmit aperture that is obtained by coherently integrating the quadratic phase change over a continuum of focal points. Thus uniform sensitivity and uniform point spread function can be achieved over a very large depth without reducing the frame rate. Numerical simulations validate our theoretical analysis and demonstrate significant promises of the new technique.

3498: Ultrasound echo processing optimized algorithms for software implementation with commercial DSPSs

Objectives: Software implementation of major functional blocks of a medical ultrasound imaging system is advantageous in field upgradeability and development cost. We present efficient methods for real time implementation of echo processing block for medical ultrasound imaging with minimum number of commercial DSPs.

The Use of the Fractional Fourier Transform With Coded Excitation in Ultrasound Imaging

Medical ultrasound systems are limited by a tradeoff between axial resolution and the maximum imaging depth which may be achieved. The technique of coded excitation has been used extensively in the field of RADAR and SONAR for some time, but has only relatively recently been exploited in the area of medical ultrasound. This technique is attractive because allows the relationship between the pulse length and the maximum achievable spatial resolution to be changed. The work presented here explores the possibility of using the fractional Fourier transform as an effective means for the processing of signals received after the transmission of linear frequency modulated chirps. Results are presented which demonstrate that this technique is able to offer spatial resolutions similar to those obtained with a single cycle duration signal.

Tissue motion analysis medical diagnostic ultrasound system and method

Accurate tissue motion systems and methods are provided. Motion of the ultrasound transducer is accounted for in estimates at tissue motion. Correcting for transducer motion better isolates localized tissue contractions or expansions, such as motion of the myocardial muscle or fibers. Accurate motion estimation is also provided by determining an angle of motion from the ultrasound data. The angle of motion is used to adjust velocity estimates, providing two-dimensional velocity vectors (i.e. motion estimates comprising motion in at least two dimensions). Movement of tissue is determined by correlating speckle or a feature represented by two different sets of ultrasound data obtained at different times. Additional aspects include tracking the location of a tissue of interest. A characteristic of strain, such as the strain rate or strain, is calculated for the tracked tissue of interest. Ultrasound data associated with different positions relative to the transducer are selected as a function of the tracking and used to determine the characteristic of strain. Motion estimates corrected for transducer motion may also be used to determine a strain or strain rate. In yet another aspect, motion estimates are generated with data from an intra-cardiac transducer array. The characteristic of strain is determined from the motion estimates. Other aspects discussed above may be used with an intra-cardiac transducer array, providing accurate motion analysis based on imaging from within the heart.

Diagnostic medical ultrasound system having method and apparatus for storing and retrieving 3D and 4D data sets

A method and system is disclosed which permits a user to save user defined viewing configuration, also referred to as a bookmark as a separately manipulatable or transferable entity without altering the underlying image data and maintaining, where desired, the association between the bookmark 200 and the underlying source image data. The disclosed system and method act to save the bookmark by saving the succession of system inputs, which, in conjunction with the system characteristics and system parameters, achieve the desired viewing configuration. Thereby, the disclosed system and method permits review of the inputs used to manipulate the image to confirm the process by which a diagnosis or anatomical measurement was made, permits the replay of a sequence for presentation or training purposes to effectively demonstrate not only the end result, but the methodology as well. The disclosed system and method further permits the user to save the system parameters as set for a desired given viewing configuration of a 4D image sequence in addition to or in lieu of saving the system inputs. In this way, the desired viewing configuration is preserved while maintaining the integrity of the underlying image data. In addition, the disclosed system and method further permit the user to maintain or terminate the association of the bookmark 200 with the entirety of the source image data, or just a portion thereof.

A log-domain /spl mu/beamformer for medical ultrasound imaging systems

A fully differential, Class-AB, log domain microbeamformer has been designed in a 60 GHz Si-Ge BiCMOS process. The demonstrated microbeamformer has four input channels and four delays, though the concept can easily be extended to any desirable configuration. The log domain, Class-AB architecture is perfect for medical ultrasound applications due to the fact that the received ultrasound signal has very low amplitude during the major part of the reception period. This leads to very low power consumption because of the Class-AB configuration. The delay-line in the microbeamformer is constructed using a cascade of low input impedance allpass filter cells. A simple implementation of the zero in the allpass filter helps to keep the overall power consumption low. The delay of each allpass filter cell is programmable through the adjustment of a tuning current. Due to the Class-AB architecture used, every source signal must be shaped by a signal preconditioning circuit before connected to the filter cells. A well-known preconditioning circuit has been modified to increase the dynamic range. The modification introduces noise cancellation as well as a method to increases the maximum signal swing. The dynamic range of one preconditioning cell is shown to increase 12.6 dB compared to the classic translinear circuit at a penalty of 15% increase in the power consumption. Signal-to-noise ratio of one allpass filter cell is typically 56.5 dB, and the global dynamic range of the same cell is typically 63.8 dB at an average power consumption of 3.5 mW when 16 input signals are connected to the filter. The power consumption at maximum signal amplitude for the microbeamformer having four input channels and four delays is 3.2 mW with a supply voltage of 2.5 V. In the intended application, the quiescent power consumption is a much better description of the average power consumption. This power consumption is 1.3 mW.

Diagnosis of breast tumors with ultrasonic texture analysis using support vector machines

This study presents a computer-aided diagnosis (CAD) system with textural features for classifying benign and malignant breast tumors on medical ultrasound systems. A series of pathologically proven breast tumors were evaluated using the support vector machine (SVM) in the differential diagnosis of breast tumors. The proposed CAD system utilized facile textural features, i.e., block difference of inverse probabilities, block variation of local correlation coefficients and auto-covariance matrix, to identify breast tumor. An SVM classifier using the textual features classified the tumor as benign or malignant. The proposed system identifies breast tumors with a comparatively high accuracy. This can help inexperienced physicians avoid misdiagnosis. The main advantage of the proposed system is that the training and diagnosis procedure of SVM are faster and more stable than that of multilayer perception neural networks. With the expansion of the database, new cases can easily be gathered and used as references. This study dramatically reduces the training and diagnosis time. The SVM is a reliable choice for the proposed CAD system because it is fast and excellent in ultrasound image classification.

Ferroelectricity: The Foundation of a Field from Form to Function

AbstractThis article highlights the major role Arthur von Hippel and the Laboratory for Insulation Research at the Massachusetts Institute of Technology played in the early development of the field of ferroelectricity in mixed oxides with the perovskite structure and, in particular, in the identification of ferroelectricity in barium titanate following its discovery in industrial laboratories in the United States during World War II.Very early optical and x-ray studies highlighted the characteristics of the ferroelectric domain structures in both ceramic and single-crystal BaTiO3, the elimination of domains at the Curie temperature TC, and the salient characteristics of the two low-temperature phase transitions. Perhaps the culmination of this work was the detailed studies of lamella 90° domains by Peter Forsbergh and the gorgeous patterns these could generate. This article also traces the manner in which the early studies contributed to whole industries based on perovskite ferroelectrics. The ceramic capacitor industry is now fabricating sophisticated, cofired multilayer capacitors (MLCs) with up to a thousand 1-µm-thick dielectric layers interleaved with base metal electrodes, addressing a market for some 1013 capacitors per year.Manufacturers of large piezoelectric transducers depend almost exclusively on perovskite-structure oxide ceramics. Navy sonar systems are major customers, but spinoff has occurred into a wide range of commercial and medical ultrasound systems. The capability of current materials has improved more than tenfold over the original BaTiO3 ceramics as a result of the effective application of molecular engineering, a strong testament to the insight of the founder of this area of study.

Piezoelectric contrast materials for ultrasound imaging

Piezoelectric ceramics and polymers can be used as a type of marker and contrast material for medical ultrasound imaging systems. High-frequency electrical signals are detected from surface electrodes when these materials are introduced into conducting media such as tissue and scanned by ultrasound imaging systems. Detected signals are applied to the imaging circuits of a modified ultrasound system such that they display a unique type of electrical image that shows the piezomaterial's polarization, shape, and position at arbitrarily high contrast compared to the conventional ultrasound acoustic image. The resulting piezoelectric image can be merged in real-time with conventional ultrasound acoustic imaging to form a composite image. This approach is of interest in the development of improved techniques for imaging medical devices that are implanted or otherwise introduced into the body.

Detection performance theory for ultrasound imaging systems

A rigorous statistical theory for characterizing the performance of medical ultrasound systems for lesion detection tasks is developed. A design strategy for optimizing ultrasound systems should be to adjust parameters for maximum information content, which is obtained by maximizing the ideal observer performance. Then, given the radio-frequency data, image and signal processing algorithms are designed to extract as much diagnostically relevant information as possible. In this paper, closed-form and low-contrast approximations of ideal observer performance are derived for signal known statistically detection tasks. The accuracy of the approximations are tested by comparing with Monte Carlo techniques. A metric borrowed and modified from photon imaging, Generalized Noise Equivalent Quanta, is shown to be a useful and measurable target-independent figure of merit when adapted for ultrasound systems. This theory provides the potential to optimize design tradeoffs for detection tasks. For example it may help us understand how to push the limits of specific features, such as spatial resolution, without significantly compromising overall detection performance.

Iterative ultrasonic signal and image deconvolution for estimation of the complex medium response

The ill-conditioned inverse problem of estimating ultrasonic medium responses by deconvolution of RF signals is investigated. The primary difference between the proposed method and others is that the medium response function is assumed to be complex-valued rather than restricted to being real-valued. Derived from the complex medium model, complex Wiener filtering is presented, and a Hilbert transform related limitation to inverse filtering type methods is discussed. We introduce a nonparametric iterative algorithm, the least squares method with point count regularization (LSPC). The algorithm is successfully applied to simulated and experimental data and demonstrates the capability of recovering both the real and imaginary parts of the medium response. The simulation results indicate that the LSPC method can outperform Wiener filters and improve the resolution of the ultrasound system by factors as high as 3.7. Experimental results using a single element transducer and a conventional medical ultrasound system with a linear array transducer show that despite the errors in pulse estimation and the noise in the RF signals, excellent results can be obtained, demonstrating the stability and robustness of the algorithm. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 266–277, 2005

Radial reflection diffraction tomography

A wave‐based tomographic imaging algorithm based upon a single, rotating, radially outward oriented transducer has been developed. At successive angular locations at a fixed radius, the transducer launches a primary field and collects the backscattered field in a ‘‘pitch/catch’’ operation. The hardware configuration, operating mode, and data collection method are identical to that of most medical intravascular ultrasound (IVUS) systems. The goal is to develop a wave‐based imaging algorithm using diffraction tomography techniques. Given the hardware configuration and the imaging method, this system is referred to as ‘‘radial reflection diffraction tomography.’’ Two hardware configurations are considered: a multimonostatic mode using a single transducer as described above, and a multistatic mode consisting of a single transmitter and an aperture formed by multiple receivers. The probe is mounted at the end of a catheter or snaking tube inserted into a part or medium with the goal of forming images of the plane perpendicular to the axis of rotation. An analytic expression for the multimonostatic inverse is derived but ultimately a Hilbert space inverse wave algorithm is used to construct images using both operating modes. Applications include improved IVUS imaging, bore hole tomography, and nondestructive evaluation (NDE) of parts with existing access holes.

Visualisation Technique for Trabecular Architecture of Bone Using Ultrasound Signals

We have proposed a new technique for visualising trabecular architecture of spongy bone using ultrasound A-mode signals from a transducer of medical ultrasound system. The technique can be established by finding a method to distinguish between bone and bone marrow. Firstly, the A-mode signal intensity was fitted by the form, A=A0exp(-ax), where A, A0, a, and x represent echo intensity, initial value of echo, attenuation factor, and distance, respectively. Then the curve was moved slightly downward or upward by multiplying with the coefficient k (0.9~1.2), and it was used as an index line to distinguish between bone and bone marrow. To clarify the validity of the proposed technique, we examined bovine bone specimen and a spongy-shaped specimen made by ceramics. The pixel size for creating architecture was 0.2 (width) × 0.15 (depth) mm for bone marrow and 0.2 × 0.3 mm for bone substance, and the pixel size differs due to the difference in wave speeds. The visualisation technique was capable to create an image size of ~10 mm depths from the surface of cortical bone. We also tried to visualise the heel bone.

Aperture size effect on ultrasonic wavefront distortion correction

The influences of aperture size on wavefront distortion correction are investigated both theoretically and numerically. A multilayer, phase-screen model is assumed to be the underlying, distorting medium. Numerical simulations were performed using three wavefront distortion correction methods: time-shift compensation (TSC), backpropagation followed by time-shift compensation (BP+TSC), and the previously proposed, multilayer, phase-screen compensation (MPSC) method. The distorted wavefronts were generated by propagating a planar wavefront through a multilayer, phase-screen model constructed with a two-dimensional (2-D) scanned map of a real abdominal slice. Performances were evaluated by L2 errors between the corrected wavefronts and the undistorted planar wavefront. Point spread functions also were calculated to evaluate the relative image quality. Theoretical analysis shows L2 error will decrease as aperture size grows when exact phase compensation (EPC) is applied, although finite errors will always exist along the edges of the corrected wavefront. Three different aperture sizes, 14.24 mm (64 elements), 28.48 mm (128 elements), and 56.96 mm (256 elements) are considered in this study. Numerical results show that the quality of wavefront with EPC is essentially limited by the aperture size, and the correction methods considered are relatively robust against the aperture size. It also shows that, for low aberration, results with MPSC and EPC are comparable. However, for high aberration, MPSC significantly outperforms EPC in suppression of L2 error and sidelobes. This study suggests that, for most medical ultrasound imaging systems, the exact structure of the distorting medium may not be necessary to be known a priori for optimal distortion correction because of the limitation imposed by finite aperture size.